Roll gap and gap error monitoring device

ABSTRACT

A controller for the width of the gap between a pair of rolls in a rolling mill, maintaining that gap constant at a predetermined level, uses two radially facing surfaces adjacent the ends of the rolls. The radial distance of one of the surfaces is adjustable as command value equivalent of desired gap width. The controller operates to maintain the distance between the surfaces constant independently from the level of adjustment of the one surface.

United States Patent 1191 Meyer June 18, 1974 15 1 ROLL GAP AND GAP ERROR 3,570,288 3/1971 Fischer et a1. 72/8 MONITORING DEVICE 3,662,576 5/1972 Girlatschek 72/21 [76] Inventor: Friedrich-Wilhelm Meyer, FOREIGN PATENTS OR APPLICATIONS Bradenburger Strasse Varrel 827.167 2/1960 Great Britain 33/182 Germany 489.287 6/1970 Switzerland 33/182 [22] Filed: May 10, 1973 P E M1 S M h rlmary .tammerltOIl e l [21] Appl- 3581837 Attorney, Agent, or Firm-Ralf H. Siegemund [30] Foreign Application Priority Data [57] ABSTRACT May 1972 Germany 2224909 A controller for the width of the gap between a pair of 52 US. (:1 72/21, 72/35, 33/182 rolls a 1 maintaining F l 511 Int. Cl B2111 37/08 a PredeFe'mmed level uses rad'any l 1 faces ad acent the ends of the rolls. The rad1al d1s- [58] Field of Search 72/21, 22, 29, 35; 33/182 tance of one of the surfaces 1s ad ustable as command 1561 zztiztzzzirizzztzfnie st828135281822221222: UNITED STATES PATENTS constant independently from the level of adjustment 2,684 00l 7/1954 Wilson 72/8 of [he one Surface 3358,485 12/1967 DeCaro et a]. 72/35 X 3,389,588 6/1968 Reinhardt et a1v 72/8 5 Claims, 5 Drawing Figures 71 P/m-ap l 1 I w= 2 16 75 2 I Par/mi] (ONT/9011f PATENTEDJUHMBM 3.817.068

SHEEI 2 0F 3 v r Fig. 2

ROLL GAP AND GAP ERROR MONITORING DEVICE BACKGROUND OF THE INVENTION The present invention relates to a device for detect ing information and representation on the gap between the working rolls of a rolling mill, so that the result may serve as input for a controller for maintaining the gap constant by means of automatic feedback control.

Rolling mills generally require control of the roll gap because the thickness of the rolled sheet stock or the like is usually to be kept within very close tolerances. The feedback control must meet significant dynamic requirements which include a fast operating actuator for adjusting the gap and which further include a pick up device detecting the thickness of the rolled stock as controlled variable in one way or another. This pick up device should operate without or with only insignificant delay so that the stock width will not vary beyond permissible limits. However, measuring strip or sheet stock thickness right at the roll gap is not accurate enough due to the deformation of the rolls during working and further due to some resilient reaction of the stock after emerging from the gap. Therefore, the strip or rolled sheet stock thickness is usually measured indirectly by detecting the roll gap in one way or another.

The different controllers for the roll gap differ primarily in the set up and design of the gap detection. A rather simple but relatively inaccurate method uses the displacement of the roll positioning plunger as representation of the gap. The inaccuracy here stems from the fact that the gap is only indirectly ascertained and roll flattening mill stand expansion and eccentricities in the support rolls render the relationship between the true gap and measured input rather unreliable. As a consequence, the measured value supposedly representing the roll gap must be subjected to numerous corrections as to all these disturbing influences.

Another method uses a spindle between the inserts of the support rolls, and the changes in spindle force are used as an (indirect) representation of the roll gap. The controller operates here to maintain the spindle force at a constant level, and, hopefully the roll gap is maintained constant therewith. This method works actually as a first order approximation, but this system uses as command input a supplemental spindle device which does not consider roll flattening, and eccentricities of the support are entered into this pick up system with the wrong sign. Thus, it is quite impossible here to provide for an optimized controller on that basis.

U.S. letters Pat. No. 3,662,576 of common assignee offers a significant improvement over the aforementioned control systems. This patent discloses pick up devices and uses inductive phenomena across the gap (or, more exactly, of axially displaced replica or the roll gap) to ascertain thetrue gap dimensions. This pick up system operates indeed satisfactorily but because of the particular inductive mode of detection, application is restricted to rolling mills with relatively low rolling speeds.

SUMMARY OF THE INVENTION It is an object of the present invention to avoid the deficiencies and drawbacks of the prior art and to provide an input for a rolling gap controller which input will not be falsified for the several reasons outlined above.

In accordance with the preferred embodiment of the invention it is suggested to define two mutually facing test and transducing surfaces, one for each roll, whereby one of these surfaces is position adjusted for establishing a positional representation of the desired width of the gap between the rolls; the distance between the said surfaces is ascertained, and the gap width controller operates to maintain that distance constant (but not zero!), independently from the desired gap width, but thereby maintaining the gap width in accordance with the level adjustment for the one surface.

It can thus be seen, that the principle of the invention resides in the avoiding of directly measuring rolling gap width. The gap width is measured subject to two fixed corrections. One correction is the position adjustment of one of the transducing surfaces in strict correspondence with the desired gap width. A level change of the former establishes therewith a change in the latter. That level is in effect subtracted from the measured distance, because one can say that the measured distance (except for the second correction) is equal to the gap minus adjusted level to the extent it differs from the particular level for a desired gap zero. The other correction is a fixed offset from zero which is added in fonn of a fixed distance. On one hand that fixed distance is the one dynamically maintained by the gap controller; on the other hand, fixed distance and the corresponding signal representation in the pick up is a fixed instrument parameter. The true measured value is thus the value resulting from that fixed (but arbitrarily selectable) distance plus the: positive or negative gap fluctuation by which the actual gap width deviates from the desired one.

The distance between the two surfaces is measured in any manner known per se such as inductively, capacitively, optically or electromechanically. The particular distance between the surfaces to be maintained constant by the gap controller is selected to obtain maximum sensitivity of the respective pick up system. The adjustable surface may be established by a micrometer pm.

DESCRIPTION OF THE DRAWINGS While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention, it is believed that the invention, the objects and features of the invention and further objects, features and advantages thereof will be better understood from the following description taken in connection with the accompanying drawings in which:

FIGS. la and lb are front views of a pair of rolls in a rolling mill with schematic representation of the production of a controller input in accordance with the preferred embodiment of the invention;

FIGS. 2 and 3 are side views of rolls with two different pick up arrangements; and

FIG. 4 is another side view of rolls in a mill stand with another pick up device.

Proceeding now to the detailed description of the drawings, FIGS. la and lb show a pair of working. rolls, 10 and 11 suitably joumalled in a stand by means of shaft ends. One or both of the rolls is adjustable in relation to the respective other one so as to define and adjust the disposition of the rolls for establishing a rolling gap Sw. Usually the adjustable one of the rolls is posi' tion controlled by means of automatic feedback control, and the detection of representation of the actual gap width in every instant is necessary for that control. The adjustment of the respective roll for that purpose is conventional and shown very schematic only. Of immediate relevancy here is the acquisition of a representation of the gap and the formation of a control signal representing the deviation of the desired gap width from the actual one.

Each roll has an annular shoulder 17 on each of its axial faces for joumalling a stationary annulus. The annuli for roll 11 are denoted by reference numeral 12, the annuli for roll are identified by numeral 13. These annuli differ in that each annulus 12 defines a radially facing surface 14 of fixed distance from the axis of roll 11, while annuli 13 each have an adjustable transducing surface portion 15. For example, a radially adjustable pin 16 projects from the annulus 13 to which it pertains, and the front end (facing radially with respect to the axis of the roll) establishes a particular distance level from the axis of roll 10; that level is an adjustable one.

Generally speaking, the distance between the transducing surface 14 of an annulus of an annulus 12 and the adjustable level 15 on the respective adjacent annulus 13 is identified by 8,. S denotes the level height of reference surface 15 as it extends above or beyond the annulus 13 so that S, O is a zero level. As stated, Sw represents the rolling gap. One or the other annulus, 12 or 13 of a facing pair contains an instrument pack for measuring the distance between first surface 14 and second surface 15. That instrument pack serves as a pick up which provides a signal representing S, and that signal is the input to the rolling gap controller.

The controller operates basically to maintain S, at a constant level. This is true regardless of the width of the actual gap between rolls l0 and 11. The various components are proportioned so that for constant 8,, Sw S, (plus, possibly, a fixed offset which has no bearing on the principle aspects considered here). In other words the level of adjusting the extent of projection of pin 16 from annulus 13 determines the desired gap width. Since S, is and remains constant, fluctuations in actual gap width Sw are reflected as deviations of S, from the constant value. As the controller operates to maintain S, constant, the gap SW is regulated thereby to assume and maintain a width equal to 8,. FIG. la actually shows S, =0, in which case Sw is likewise zero, and the controller maintains gap width zero dynamically. Normal operating conditions are shown in FIG. lb.

After having explained the concept of the invention on basis of the schematic illustration of FIGS. 1a and lb, I turn to FIG. 2 showing the transducing and gap detecting system in greater detail. Annulus 13 is shown with a carrier 18 from which projects pin 16. The carrier arms may serve as mount for the annuli to prevent them from following the rotation of the respective rolls on which they are journalled. Carrier 18 will be particularly provided with means, such as a micrometer or the like to adjust the level of the operating and transducing surface 15 which defines a datum or reference plane. The annulus 12 is provided with an analogously constructed carrier for supporting a pick up with an operating and detection surface 14. The pick up gap 8, is defined by the distance between surfaces 14 and 15 and one or the other carrier may include inductive, capacitive, optical or electromechanical means to respond to that gap.

Turning now to FIG. 3, the particular example shown here obviates the need for one annulus, and the one surface (14) is defined here as the periphery of the shoulder 17. The annulus 13 is provided as before. In case the pick up operates on basis of electromagnetic induction a demagnetizing device 19' should be provided in order to suppress disturbances resulting from external magnetic stray fields.

The example of FIG. 4 shows the definition of the datum planes for gap pick up by means of journals for the rolls. The supports 21 and 22 for the rolls are mounted in the stand 25. The support 21 for the lower roll 10 is provided with a transducer 23 from which projects the adjustable pin 16. The other, oppositely positioned support 22 for the upper roll 11 carries a means for defining the surface 14. Reference numeral 30 identifies the adjustment for the lower roll for adjusting the rolling gap.

It can thus be seen that the inventive transducing and pick up system does not directly measure the actual gap. What is measured is a basically arbitrarily selectable distance S,, and the controller operates to keep that distance constant. The distance S, can be interpreted as an error-distance plus a constant position bias. The distance S, is basically selected to have the transducer pick up operating in a range of maximum sensitivity. As such, the transducer signal representing S, is a controller input combining a gap error signal plus constant bias. The signal representing the distance S, is exactly equal to that constant bias when the actual roll gap' equals the desired gap.

The desired gap as such is not represented in S, but it can be seen, that any desired gap can be maintained through control towards a constant S, upon adjusting the level of reference surface 15 (height of pin 16 as projecting from annulus 13) to a particular level. This way the thickness of the rolled stock can be maintained constant, regardless of what that thickness value is. The controller has the same dynamic range as far as its input and input signal processing isconcemed.

One can, however, interpret the device as a whole as a true gap measuring device. The actual gap width is given by S, S, a constant bias representing S, at zero gap error. S, is the projection of the pin and aside from its adjustment, it may be represented as a measured value. S, is ascertained on a running basis by the transducer arrangement, and the constant bias can be predetermined as the value 8,, actually provided by the measurement upon S Sw. This is part of the initial calibration procedure. Only S, will vary during operation, and that variation represents the fluctuation of the true gap width. The desired value (8,) may be separately indicated, e.g., digitally.

The inventive device has a number of advantages. The desired gap width is mechanically adjustable and accuracy here is determined only by the adjustment as such and is not influenced by the rolling process. As similar devices operate on both ends of each roll, the rolls can be maintained in parallel by means of the control for each shaft end and journal. Journalled annuli or truly stationary support devices for the pick up can be used, the latter being of advantage for high rolling speeds. The accuracy of the measurement is not influenced by cooling. Also, calibration is rather simple. 8, 0 is established for engaging rolls, and S, follows the gap as they are separated. Conversely, upon increasing S under the closed loop conditions, the device will operate as follower controller seeking or maintaining dynamically the adjusted gap. Consequently, an exchange of rolls is not difficult and will pose no problems as to control with a new set of rolls.

The invention is not limited to the embodiments described above but all changes and modifications thereof not constituting departures from the spirit and scope of the invention are intended to be included.

I claim:

1. Apparatus for providing a control signal for a controller controlling the width of the gap between a pair of rolls in a rolling mill for maintaining that gap constant at a predetermined level, comprising first means defining a first radially facing surface on one of the rolls, but axially displaced from the working surface of the one roll;

second means defining a second, radially facing surface on the other one of the rolls, facing the first surface, and

third means included in the second means for mechanically adjusting the radial distance of the second surface from the axis of the other roll within a range of levels, whereby one of the levels represents zero gap width; the controller operating to maintain the distance between. the first and second surfaces constant independently from the level of adjustment of the second surface by operation of the third means.

2. Apparatus as in claim 1, the second means including a carrier joumalled on one shaft end of the other roll and carrying an adjustment pin having an axial face, facing radially with respect to the axis of the other roll and serving as the second surface.

3. Apparatus as in claim 2, the carrier being part of an annulus joumalled on said shaft end.

4. Apparatus as in claim 2, the carrier being mounted on the stationary journal for the other roll.

5. Apparatus as in claim 1, the one roll provided with a cylindrical transducer surface serving as the first surface.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 817 I068 Dated Jllvl'lev l3 1974 Inventor(s) Friedrich-Wilhelm Meyer It is certified that error appears in the above identi'fied patent and that said Letters Patent are hereby corrected as shown below:

[ 73 Assignee: Vereinigte Flugtechnische Werke e Fokker Brernen, Germarly Signed: and sealed this 11th day of March 1975.

(SEAL) Attest:

C. MARSHALL DANN Commissioner of Patents and Trademarks RUTH c. MASON, Attesting Officer 

1. Apparatus for providing a control signal for a controller controlling the width of the gap between a pair of rolls in a rolling mill for maintaining that gap constant at a predetermined level, comprising first means defining a first radially facing Surface on one of the rolls, but axially displaced from the working surface of the one roll; second means defining a second, radially facing surface on the other one of the rolls, facing the first surface, and third means included in the second means for mechanically adjusting the radial distance of the second surface from the axis of the other roll within a range of levels, whereby one of the levels represents zero gap width; the controller operating to maintain the distance between the first and second surfaces constant independently from the level of adjustment of the second surface by operation of the third means.
 2. Apparatus as in claim 1, the second means including a carrier journalled on one shaft end of the other roll and carrying an adjustment pin having an axial face, facing radially with respect to the axis of the other roll and serving as the second surface.
 3. Apparatus as in claim 2, the carrier being part of an annulus journalled on said shaft end.
 4. Apparatus as in claim 2, the carrier being mounted on the stationary journal for the other roll.
 5. Apparatus as in claim 1, the one roll provided with a cylindrical transducer surface serving as the first surface. 